1. Field of the Invention
The present invention relates generally to a gas treatment system and method for carrying out a plasma treatment with respect to, e.g., a semiconductor waver.
2. Description of the Prior Art
In a process for producing a semiconductor device, there is a process for treating a semiconductor waver (which will be hereinafter referred to as a xe2x80x9cwaferxe2x80x9d) serving as a substrate to be treated, using plasma. This is carried out by introducing a treatment gas into a vacuum vessel having a wafer mounting table and supplying electromagnetic energy to the treatment gas to produce plasma. For example, as such a process, there are deposition and etching. As a technique for producing plasma, there are the ECR system for utilizing the electromagnetic cyclotron resonance which is the interaction between microwaves and a magnetic field, the ICP system for supplying electric and magnetic fields to a treatment gas from a coil wound onto a dome-shaped vessel, and the parallel plate system for applying a high-frequency power between a pair of plates facing each other.
In such a plasma treatment, particles produced in plasma, e.g., radicals, have different functions, such as deposition and etching, in accordance with the kind of the particles, so that it is considered that radicals play an important role in the treatment on a wafer. Therefore, there are disclosed a method for estimating the density of radicals during the production of plasma, and a method for controlling the microwave output by the value thus obtained. As a method for estimating the density of radicals, there are a laser induced fluorescence method (LIF method) for irradiating plasma with laser light to allow molecules to absorb the light to emit fluorescence to estimate the density of radicals on the basis of the measured value of the fluorescence, and a method for detecting the variation in spectrum of an infrared semiconductor laser beam to measure the density of radicals in a vacuum vessel.
However, since the above described LIF method is a method for measuring fluorescent molecules, it is not possible to estimate the density of a non-fluorescent kind of radicals, and it is impossible to measure high-order radicals having a great molecular number, so that there is a problem in that it is not possible to precisely carry out a process control.
Also in the method for measuring the radical density on the basis of the variation in spectrum of the infrared semiconductor laser beam, although it is possible to measure low-order radicals since the spectrum caused by radicals is known, it is impossible to measure high-order radicals having a great molecular number.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a system and method capable of estimating the kind and density of, e.g., radicals, to carry out a good treatment, e.g., a treatment having a small dispersion between substrates to be treated.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a gas treatment system for supplying a treatment gas into a vacuum vessel to carry out a predetermined treatment for a substrate to be treated, the system comprising: electron adding means for emitting electrons to the treatment gas extracted from the vacuum vessel and for causing electrons to adhere to particles in the treatment gas; mass spectrometry means for determining the kind of negative ions of the particles, to which electrons adhere, by the electron adding means; density estimating means for estimating the density of the particles in the treatment gas corresponding to the determined negative ions, on the basis of the measured value of the number of the negative ions determined by the mass spectrometry means; and a control part for controlling a process condition, which influences the state of the treatment gas in the vacuum vessel, on the basis of the estimated result of the density of the particles estimated by the density estimating means.
The density estimating means may vary the magnitude of electron energy emitted from the electron adding means, to derive the variation in measured value of the negative ions of the particles, to use data corresponding to the peak value of the measured value as the estimated result of the density of the particles. The mass spectrometry means preferably has a gas extracting port which is movable in the vacuum vessel. The electron adding means may be connected to the vacuum vessel via a bellows which is retractable with respect to the vacuum vessel. The process condition may be at least one of the magnitude of energy applied to the treatment gas, the pressure in the vacuum vessel, and the flow rate of the treatment gas. The control part may carry out a feedback in real time on the basis of the estimated result of the density of the particles estimated by the density estimating means, to control the process condition. The control part may set and control the process condition with respect to a subsequent product substrate to be treated, on the basis of the estimated result of the density of the particles estimated by the density estimating means with respect to a test substrate to be treated.
In addition, according to the present invention, the particles in the treatment gas, to which electrons adhere, may be radicals, molecules or atoms. The magnitude of electron energy emitted from the electron adding means is changed to derive the relationship between the magnitude of electron energy and the measured value of the particles, so that the density of the particles can be estimated on the basis of the derived result.